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A 160 mm f/6.5 binocular telescope

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#1 ThomasM

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Posted 02 April 2010 - 06:14 AM

This is just a plan, but may be you find it interesting. For almost two years I am thinking to construct a quite large binocular telescope. Presently I use a 2x115 mm bino, which is very nice, but for deep sky observing the aperture is just at the limit what is needed, e.g. to show spiral structure in the largest galaxies (M51, M33)

- So why a 160 mm f/6.5 binocular?

- binocular viewing can give breathtaking views
- 160 mm binocular corresponds to approximately 200 mm monocular, so it is already a deep sky telescope
- 160 mm is probably the biggest aperture which can be build as a reasonable light-weight telescope that can be easily transported and mounted in a few minutes

So the key idea of the project is getting a maximum of optical performance with a lightweight telescope

Here are the characteristics of my planed 160 mm f/6.5 binocular telescope

- two 160 mm apochromatic oil spaced triplet lenses, focal length 1050 mm giving up 2,5 degree field of view
- lightweight carbon tubes
- erecting mirror system (EMS) for 2” eyepieces with 97 per cent total transmission
- estimated weight of the bino 12-13 kg ( both tubes), with mount and tripod less than 20 kg


I hope to get it finished until the end of the year


Thomas

#2 roadi

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Posted 02 April 2010 - 09:20 AM

Not to take away your excitement, but I think you are rather optimistic about the weight, not only the instrument alone, but also total with mount! ;)

My 6" achro bino weighs exactly 15kg. A grob estimation is: Your Triplet has one more lens element vs an doublet, wich add about 50% to the weight of the lens assemby, add to this further 13% "160mm = about 13% more area and weight, assumed same thicknes of the glas"
Aluminum tubes of 150mm diam, 650mm length and 3mm thick is about 2.2 kg x 2 = 4.4kg wich would be the max you could save in weight but add to this the weight of the CF tubes.
Then comes the hardware you need atacking the tubes with each other!
I think you'll end well over 15Kg for the instrument alone. A good and stable forkmount will at add further 10-15kg then comes the tripod! ;)
Nevertheless it will be an awesome binoscope! :bow:

#3 ThomasM

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Posted 02 April 2010 - 10:34 AM

My 6" achro bino weighs exactly 15kg. A grob estimation is: Your Triplet has one more lens element vs an doublet, wich add about 50% to the weight of the lens assemby, add to this further 13% "160mm = about 13% more area and weight, assumed same thicknes of the glas"
Aluminum tubes of 150mm diam, 650mm length and 3mm thick is about 2.2 kg x 2 = 4.4kg wich would be the max you could save in weight but add to this the weight of the CF tubes.
Then comes the hardware you need atacking the tubes with each other!
I think you'll end well over 15Kg for the instrument alone. A good and stable forkmount will at add further 10-15kg then comes the tripod! ;)
Nevertheless it will be an awesome binoscope! :bow:


Rodi,

I hope too that it will be an awsome binoscope and I easily understand your scepticism about the weight.

Now doubt, it will be difficult to get below 20 kg including mount and tripod.

How do can it work?

- the lenses, are really light- at least for this size- only 3,5 kg each. With air spaced triplets it seems impossible, but oil spaced can be thinner because all three elecments are in direct contact.

- the carbon tubes are only 0.5 kg each, they are already delivered

- the two tubes are almost in direct contact fixed only by a few light but stable aluminum pieces in between

- the two mirror systems adds another 2 kg, so instrument alone will be below 13 kg

- I will not use a fork mount, the mount will be similar to that of big binos, like Kowa Highlander or the Fujinon 150mm bino (see http://www.intercon-...wa_highlander/), but more stable
It will be mounted on a carbon tripod (3kg), which also exists already

All in all, drawings for the construction are almost finished and I hope that everything works out as planed.

Thomas

#4 Ziggy943

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Posted 02 April 2010 - 11:06 AM

I am wondering who is the source for the lenses. What are you expecting the cost to be?

Being bino's I take it that this is intended as a visual Deep-Sky instrument. I guess I have to ask WHY?????

#5 GShaffer

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Posted 02 April 2010 - 12:24 PM

Given what I have seen and heard here I believe the only good answer is "why not?" :)

#6 CounterWeight

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Posted 02 April 2010 - 12:33 PM

That sounds like quite a wonderful bino-scope, I'd expect some amazing to phenominal views with it! Good to try for lowest possible weight, it will be interesting to see when all is done.

In my wildest imaginings I've thought about someday getinng another 160ed and making a bino - but for now it remains wild imaginings. I'd love to know how this turns out and what the views are like.

Best of luck with the project :)

[edit] doing the money math, that is an extremely reasonable way to get ~200mm equivelant apo! hmmm never thought about it that way, but 200mm Apo's are way over double the cost of 2 160's...]

#7 roadi

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Posted 02 April 2010 - 12:41 PM

Thomas,
Thats an exciting project you are going into! It will almost be a GrabN Go giant bino, surprisingly lightweight!

Hope it all works out for you and hope to hear more about it! ;)

By the way, where do you get these EMS? any homepage?

#8 ThomasM

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Posted 02 April 2010 - 02:56 PM

Thanks to all for the best wishes for the project,

Rodi,

the EMS erecting mirror system will be manufactured in Japan:

http://www.page.sann...oto/index-e.htm

they are available with different options in different size, the 2 inch version can provide a large field of view, however, depending on the f-number of the telescope large mirrors may be needed.

I choose the 2" inch version since I will get wide field views which is at least equivalent to that of the huge 150 mm Fujinon bino, while also wide ultra field eyepiece can be used for deep sky viewing and planetary observation up to 250 x magnification.

Thomas

#9 dscarpa

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Posted 02 April 2010 - 03:02 PM

It would be a incredible lunar planetary-scope! I'd be happy with half of it. David

#10 roadi

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Posted 02 April 2010 - 03:06 PM

Thanks for the link Thomas ;)

#11 Ziggy943

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Posted 02 April 2010 - 03:28 PM

That sounds like quite a wonderful bino-scope, I'd expect some amazing to phenominal views with it! Good to try for lowest possible weight, it will be interesting to see when all is done.

In my wildest imaginings I've thought about someday getinng another 160ed and making a bino - but for now it remains wild imaginings. I'd love to know how this turns out and what the views are like.

Best of luck with the project :)

[edit] doing the money math, that is an extremely reasonable way to get ~200mm equivelant apo! hmmm never thought about it that way, but 200mm Apo's are way over double the cost of 2 160's...]


I don't understand why 2 x 160mm ~ 1 x 200mm. Each 160 goes into one eye and I don't think it's cummulative. You still only have the resolution of one. You will have some constrast gain and probably a reduction in the 'floater' nuisance.

The combined light-gathering is actually closer to a 9". So you would have the brightness of a bino on a 9" but the resolution of the 160. Bino on a 9" you also have the resolution of a 9".


The brain (my brain) doesn't make things half as bright when I close one eye. That's not where a gain is. I can understand the novelty of it and if it's something somebody really wants, well then... great.

#12 CounterWeight

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Posted 02 April 2010 - 04:58 PM

A few things come to mind, esp compared to a conventional binoviewer. I had a Denk BV'er for a while. Folks seem to like them, I did, but sold them all the same. So 2-eyed viewing - I think that's what this project / idea is about? There is some differce in the light throughput to each eye in a conventional binoviewer on a mono scope vs. that of an actual binoscope, right? I've no idea what formula Thomas used for the eq apeture - but if it's so, then great. An interesting variant would be to collimate both tubes into one eyepiece view?


Heck, I encourage experimentation, asking questions, trying stuff out... when nobody can be physically damaged. It isn't knowledge until you actually do it. Like what Reimann did with Euclid, or Bell with 'relativity', or me with respect to "very hot" hot sauce(I was almost damaged by that experiment), or that daredevil whose famous last words were "watch this! (termianlly damaged)" The more knowledge in the pool the better, even if it 'dont try that-

#13 roadi

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Posted 02 April 2010 - 05:55 PM

I never heard about a gain of 40% in lightgathering/throughput on a bino scope vs cyclop mode, but I have heard and read of a gain of about 40% in detecting low contrast planetary features over monokular mode. Thats a huge difrence in performance! ;)

#14 Ziggy943

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Posted 02 April 2010 - 06:56 PM

I never heard about a gain of 40% in lightgathering/throughput on a bino scope vs cyclop mode, but I have heard and read of a gain of about 40% in detecting low contrast planetary features over monokular mode. Thats a huge difrence in performance! ;)



Where did you get those numbers? I don't see them here anywhere.

#15 CounterWeight

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Posted 02 April 2010 - 09:06 PM

read carefully the first post...


- binocular viewing can give breathtaking views
- 160 mm binocular corresponds to approximately 200 mm monocular, so it is already a deep sky telescope
- 160 mm is probably the biggest aperture which can be build as a reasonable light-weight telescope that can be easily transported and mounted in a few minutes




#16 Ziggy943

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Posted 02 April 2010 - 10:49 PM

read carefully the first post...



- binocular viewing can give breathtaking views
- 160 mm binocular corresponds to approximately 200 mm monocular, so it is already a deep sky telescope
- 160 mm is probably the biggest aperture which can be build as a reasonable light-weight telescope that can be easily transported and mounted in a few minutes




You're assuming that's true. I don't believe that's true at all. Quoting it doesn't make it true.

It's not cummulative. You can divide the light but you can't add them. If you add the beams you're back to a single eyepiece. The 200 will be brighter and have more resolution. How does that correspond "approximately" to a "200 mm"? Based on what I'd like to know?

#17 ThomasM

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Posted 03 April 2010 - 03:37 AM

Ziggy,

the statement that a 160 mm binoscope correspond to aprroximately 200 mm mono holds only for low contrast objects, such as most deep sky objects. Your right, the light does not add, but if you look with two eyes, the noise is reduced and weaker objects become visible.
The gain is a factor 1.4 in area, more precisely square root of 2, which is almost equivalent with a factor 1.2 in diameter.
More details are given in the book 'binoclular astronomy',

here is link,

http://www.amazon.de..._pt#reader-page

page 3

The angular resolution will certainly not increase, but even for planetary viewing often more details can be seen, since finer contrast steps are becoming distinguishable. Furthermore, true binoviewing helps if the seeing is not optimal. However, for plantetary viewing I would not dare to give a factor how you actually gain over viewing with a single scope.


Thomas

#18 roadi

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Posted 03 April 2010 - 04:46 AM

Ziggy943,
About the contrast gain of 40%, I have my reference from the book "Observing and Photographing the Solar system" author: Thomas A Dobbins, Donald C Parker and Charles F Capen.

I havn't done actual measuring my self, "don't know how" but relating to my own findings viewing planets both monocular and binocular, I have no reason to doubt that claim! I can make out subtible details on the planets wich I can't monocular.
If the contrast gain in percentage is correct and you want to take advantage of the binomode, then you'll need 226mm aperture to equal a 160mm binoscope in lightgrasp. On the resolution part you are correct. Besides those wich Thomas allready mensioned, you have the advantages using 2" EP's in the binoscope wich you can't take full advantage of in most binoviewers if widest possible field is desired.

Thomas,
Interesting book, I'll have to read it! :)


#19 EdZ

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Posted 03 April 2010 - 06:57 AM

That sounds like quite a wonderful bino-scope, I'd expect some amazing to phenominal views with it! Good to try for lowest possible weight, it will be interesting to see when all is done.

In my wildest imaginings I've thought about someday getinng another 160ed and making a bino - but for now it remains wild imaginings. I'd love to know how this turns out and what the views are like.

Best of luck with the project :)

[edit] doing the money math, that is an extremely reasonable way to get ~200mm equivelant apo! hmmm never thought about it that way, but 200mm Apo's are way over double the cost of 2 160's...]


I don't understand why 2 x 160mm ~ 1 x 200mm. Each 160 goes into one eye and I don't think it's cummulative. You still only have the resolution of one. You will have some constrast gain and probably a reduction in the 'floater' nuisance.

The combined light-gathering is actually closer to a 9". So you would have the brightness of a bino on a 9" but the resolution of the 160. Bino on a 9" you also have the resolution of a 9".


The brain (my brain) doesn't make things half as bright when I close one eye. That's not where a gain is. I can understand the novelty of it and if it's something somebody really wants, well then... great.


First of all you need to calculate based on Binocular Summation, not on the sum of all the aperture, and certainly not on the summation factor times the diameter of the aperture. The concept of Binocular Summation is well documented and extensive discussion can be found in either the Binocular forum or the Binoviewer forum. Look in the Best Of threads links or the Resources links.

Binocular summation shows that when using two apertures delivering light to two receptors (the two eyes), the summation effect is sqrt of 2 ( the two eyes) times the area of light delivered from one aperture to one eye. So your effective aperture is sqrt of 160x160x1.414 = 190mm. Still not to shabby, but the combined light gathering is more like 7.5", not 9".

Binocular Limiting magnitude has been tested extensively and compared to monocular LM and found to follow the sqrt 2 summation factor. You can see approx 0.4 magnitude deeper when using same aperture thru two eyes. Numerous tests by numerous individuals using a variety of instruments shows results ranging from 0.2mag to 0.4mag gain.

Resolution using two eyes will be improved over that of one eye. This is almost certainly a result of greater signal to noise and two receptors where one is canceling out noise seen in the other. I have found after many tests on resolution targets and stellar sources, a gain of not much more than 10-15% in resolution. So, when using binocular vision, resolution will not be based on the 160mm single aperture, but will be improved, although not by the factor of sqrt2. The binocular vision resolution will be similar to that of a 180mm scope (+/-) used in mono. However, the ultimate resolution, resolution at the Rayleigh Limit, wil not be greater than can be achieved with the same size scope.

Contrast is said to follow the sqrt 2 form, but anyone that finds a realistic way to actually test that, please let me know. Same instrument (one eye vs two) on a variety of Sb objects is probably not a good test due to the variation in core vs extended total brightness from one object to another. Probably the best way is a variety of instrument sizes on the same surface brightness extended object. Even at that, it would be quite subjective.

You would need an 9" scope with binoviewers to get the same effective light gathering and image brightness (at same power) as this setup. The scope with binoviewers would have much better 9" stellar resolution.

With all that, you've gotta like the views thru a pair of 160mm binoculars.

edz

#20 Mr. Bill

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Posted 03 April 2010 - 05:11 PM

Signal theory....

The signal to noise ratio (contrast)of extended objects is equal to...

The square root of the sum of the number of detectors, or sq rt of 1+1=2 or 1.414. In other words, the contrast of two eyed observing is equal to 41% more than one eyed for the same apertures.

:cool:

#21 ThomasM

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Posted 04 April 2010 - 09:49 AM

.....
Resolution using two eyes will be improved over that of one eye. This is almost certainly a result of greater signal to noise and two receptors where one is canceling out noise seen in the other. I have found after many tests on resolution targets and stellar sources, a gain of not much more than 10-15% in resolution. So, when using binocular vision, resolution will not be based on the 160mm single aperture, but will be improved, although not by the factor of sqrt2. The binocular vision resolution will be similar to that of a 180mm scope (+/-) used in mono. However, the ultimate resolution, resolution at the Rayleigh Limit, wil not be greater than can be achieved with the same size scope.

....
You would need an 9" scope with binoviewers to get the same effective light gathering and image brightness (at same power) as this setup. The scope with binoviewers would have much better 9" stellar resolution.
...

edz


Ed,

your statement that in practice you gain 10-15 % in resolution with a bino was new to me, so I can expect that a 160 mm bino is almost equivalent to 180 mm mono for moon and planetary observation while for deep sky objects I can expect approximately 200 mm (compared to a Newton telescope, for a refractor it is somewhat smaller, 192 mm).
Both sounds very nice.

To my mind the most interesting point is, however, that binocular telescopes give a more natural and impressive view of the sky. That's why I am trying to construct a rather large but still portable bino.

Thomas

#22 zdravko

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Posted 04 April 2010 - 10:31 AM

Thomas congratulations on 160 F/6,5 APO bino scope project.
I own a 120mm F/5 achro bino scope and a 150mm F/6 achro and a smaller 76mm F/6 APO are in progress.So I'm familiar with views through a binoscope.I can confirm all the theory what had been said about contrast and resolution gain.
But for me the purpose of a large bino sope is is observing the wide field skies with both eyes.And such an instrument can also go from very low to very high powers with diferent eyepices.And no long focus big refractor can do that, even if it has a few precent better resolution.And 2,5 degres of 160mm APO view will be a dream comme true for you.
I just hope you can do it cheaper than to buy a FUJI 150mm apo binocular.
Just dont forget to post somme pictures as the project progresses.

P.S.Where are you going to buy the lenses ??

#23 Ziggy943

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Posted 04 April 2010 - 08:18 PM


.....
Resolution using two eyes will be improved over that of one eye. This is almost certainly a result of greater signal to noise and two receptors where one is canceling out noise seen in the other. I have found after many tests on resolution targets and stellar sources, a gain of not much more than 10-15% in resolution. So, when using binocular vision, resolution will not be based on the 160mm single aperture, but will be improved, although not by the factor of sqrt2. The binocular vision resolution will be similar to that of a 180mm scope (+/-) used in mono. However, the ultimate resolution, resolution at the Rayleigh Limit, wil not be greater than can be achieved with the same size scope.

....
You would need an 9" scope with binoviewers to get the same effective light gathering and image brightness (at same power) as this setup. The scope with binoviewers would have much better 9" stellar resolution.
...

edz


Ed,

your statement that in practice you gain 10-15 % in resolution with a bino was new to me, so I can expect that a 160 mm bino is almost equivalent to 180 mm mono for moon and planetary observation while for deep sky objects I can expect approximately 200 mm (compared to a Newton telescope, for a refractor it is somewhat smaller, 192 mm).
Both sounds very nice.

To my mind the most interesting point is, however, that binocular telescopes give a more natural and impressive view of the sky. That's why I am trying to construct a rather large but still portable bino.

Thomas


That also caught my eye.

Ed, are you saying that a 160mm bino can resolve closer double stars?

Isn't what you're saying a contradiction? A gain of 10-15% but the same Rayleigh limit. Where is the gain?

#24 EdZ

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Posted 04 April 2010 - 09:00 PM

The measured gain was recorded with dozens of instruments using USAF charts, but I could not record any more gain at the Rayleigh limit. If a resolution reading is taken with one eye at (say for instance using a 100mm scope or binocular) 4 arcsec is observed, than again taken with two eyes, the reading could be reduced, without increasing power, to 3.8 or 3.7 arcsec. However, once the power was raised up to about 1mm to .75mm exit pupil, at which point readings reached the Rayleigh limit, no further gain could be realized by observing with two eyes.

So my comment states, as long as you are observing below the Rayleigh limit, you can reailze some 10%-15% resolution gain by using two eyes without increasing power. But, as you approach the Rayleigh limit, the scope simply cannot resolve any better than that, regardless of using two eyes or one.

The resolution gain is realized when there is some room for improvement and when using two eyes gives the benefit of signal/noise.

edz

#25 Ziggy943

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Posted 04 April 2010 - 10:10 PM

All of the results are based on test charts? What about the question of double stars?

I find it interesting that the result is non linear, i.e., the binocular has an advantage at less than highest resolution which it gives up at higher powers. That is unexpected.






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